The present invention relates to the provision of breathable backsheets for use in absorbent articles which are activated when contacted with liquids to prevent garment wet through.
The primary consumer needs which underlie development in the absorbent article field, in particular catamenials is the provision of products providing both a high protection and comfort level.
One means for providing consumer comfort benefits in absorbent articles is by the provision of breathable products. Breathability has typically concentrated on the incorporation of so called xe2x80x98breathable backsheetsxe2x80x99 in the absorbent articles. Commonly utilised breathable backsheets are microporous films and apertured formed films having directional fluid transfer as disclosed in for example U.S. Pat. No. 4,591,523. Both these types of breathable backsheets are vapour permeable allowing gaseous exchange with the environment. This thereby allows for the evaporation of a portion of the fluid stored in the core and increases the circulation of air within the absorbent article. The latter is particularly beneficial as it reduces the sticky feeling experienced by many wearers during use, commonly associated with the presence of an apertured formed film or film like topsheet, particularly over extended periods of time. This is a result of topsheets designed to achieve a clean and dry appearance. These topsheets tend to be smooth thereby minimising the build up of fluid on the surface of the topsheet. However, these benefits are achieved at the expense of comfort, particularly under hot and humid conditions, when due to their smooth surface texture they tend to become sticky to the skin.
However, the main drawback associated with the use of breathable backsheets in absorbent articles is the negative effect on the protection level performance, by leakage known as wet through onto the users garment. Although, breathable backsheets in principle only allow the transfer of materials in the gaseous state, physical mechanisms such as extrusion, diffusion and capillary action may still occur and result in the transfer of the fluids from the absorbent core through the backsheet and onto the users garments. In particular, these mechanisms become more dominant if the product is utilised during physical exertion, or for heavy discharge loads or over extended periods of time. Thus, whilst the incorporation of breathable backsheets in absorbent articles is highly desirable from a comfort standpoint, since the primary role of a backsheet still remains the prevention of liquid leakage, such breathable backsheets cannot be satisfactorily incorporated into products.
The problem of wet through onto users garments due to the incorporation of such breathable backsheets in absorbent articles has indeed also been recognised in the art. Attempts to solve the problem have mainly resided in the use of multiple layer backsheets such as those illustrated in U.S. Pat. No. 4,341,216. Similarly EPO 710 471 discloses a breathable backsheet comprising an outer layer of a gas permeable, hydrophobic, polymeric fibrous fabric and an inner layer comprising an apertured formed film having directional fluid transport. The backsheet construction preferably has no liquid transport or wet through under certain specified test conditions. Also EPO 710 472 discloses a breathable backsheet consisting of at least two breathable layers which are unattached to one another over the core area. The backsheet construction preferably has no liquid transport or wet through under certain specified test conditions.
U.S. Pat. No. 4,713,068 discloses a breathable clothlike barrier for use as an outer cover for absorbent articles. The barrier comprises at least 2 layers, a first layer having a specified basis weight, fibre diameter and pore size and a second layer comprising a continuous film of polyvinyl alcohol having a specified thickness. The barrier also has a specified water vapour transmission rate and level of impermeability.
However, none of the above proposed solutions have been able to provide a fully satisfactory solution to the problem of breathable backsheet wet through under all conditions. Furthermore, another problem associated with the exemplified multi layer backsheets is an increase in total thickness of the product and a reduction in the flexibility, both of which result in a consumer noticeable reduction in product comfort.
An alternative proposed solution to the problem of breathable backsheet wet through relates to the improvement of the absorbent material such that little or no liquid comes into contact with the backsheet, thereby preventing wet through. This is typically achieved by increasing the amount of absorbent material in the article. However, this results in an absorbent article which is extremely thick which is highly undesirable from a consumer comfort standpoint. Hence, the absorbent article whilst having the required protection level and still maintaining some comfort benefits by the presence of the breathable backsheet, suffers from a lack of comfort from a different source, in this case the increased dimensions of the article.
In addition the above solution also results in a reduction in the flexibility of the article, particularly evident as an increase in the cross section stiffness. It is however also well established that in order to be comfortable for the wearer absorbent articles need to be cross sectionally flexible. It is believed that the more cross sectionally flexible an absorbent article is, the less will it be noticeable to the wearer. Thus flexibility is another highly desirable comfort requirement of modem absorbent articles.
EPO 705 583 and EPO 705 584 propose longitudinally flexible absorbent articles which are vapour permeable. However, the exemplified absorbent articles are typically very thin and do not address the absorbency capacity of the article or the problem of wet through.
U.S. Pat. No. 5,447,788 discloses a porous nonwoven liquid activated barrier suitable for use in absorbent articles. The barrier includes a fibrous nonwoven web in which at least 50% of the fibres are prepared from a liquid swellable polymer which is not significantly soluble in water such as swellable polyvinyl alcohols. In the presence of water the polymers swell to an extent sufficient to substantially block the passage of liquid through the fibrous nonwoven web. However, from the data given in the patent, the passage of liquids is not substantially blocked and thus these webs do not eliminate the wet through problem.
Consequently, as the incorporation of breathable backsheets in absorbent articles results in reduction of the protection level, further desirable product comfort modifications such as reducing the thickness of the product and improving the flexibility of the product which would further acerbate the problem, may not be incorporated in the absorbent article. Thus, there exists a dichotomy in the means available to provide increased consumer comfort in absorbent products and acceptable protection levels.
It is therefore an objective of the present invention to provide an absorbent article having improved comfort, by the provision of breathability throughout the absorbent article which continues to maintain an acceptable level of protection.
It has now been found that this objective may be achieved by the provision of an article having a breathable backsheet which comprises at least one air permeable layer or apertured layer, such as an apertured formed film woven or nonwoven, which comprises and is preferably coated with a non soluble, liquid swellable material.
An advantage of the present invention is that the backsheet layer when in the dry state allows the transfer of moisture vapour and air and, in its wet state after swellage, the layer maintains at least a degree of moisture vapour permeability whilst preventing the transfer of liquids.
The present invention relates to absorbent articles such as diapers, sanitary napkins, panty liners incontinence products and the like. Typically such products comprise a liquid pervious topsheet, an absorbent core and a backsheet. The present invention is characterised in that the backsheet is a breathable backsheet and comprises at least one air permeable or apertured layer, said layer having an upper surface, a lower surface and an inner surface. According to the present invention at least one of the surfaces of the apertured backsheet layer has at least one region thereon, wherein said region of said surface comprises, and preferably is coated with, a non soluble, liquid swellable material. The present invention thus provides an absorbent article product which provides circulation of water vapour and air through the product when and where it is dry and preferably maintains water vapour permeability throughout the use of the product. Moreover, by the application of a swellable material onto the apertured backsheet layer, preferably as a coating, the present invention also provides absorbent articles having a reduced tendency to exhibit garment wet through.